The invention relates to a hydrocarbon conversion process for use in petroleum refineries. The invention more specifically relates to a novel hydrotreating process flow scheme intended to simultaneously improve the cold flow properties of diesel fuel and to reduce the aromatic hydrocarbon content of jet fuel and diesel boiling range components of a single broad boiling point range feed. Such processes are referred to as catalytic hydrodewaxing and aromatics saturation processes.
Hydrotreating processes are used commercially in a large number of petroleum refineries. They are used to process a variety of multicomponent feeds ranging from light naphthas to very heavy crude oil residual fractions. In general the hydrotreating processes improve the quality of the material being processed as by increasing the hydrogen to carbon ratio of the materials or by removing sulfur and nitrogen. The significant economic utility of hydrotreating processes has resulted in a large amount of developmental effort being devoted to the improvement of these processes and to the development of better catalysts for use in the processes.
U.S. Pat. No. 4,917,789 issued to J. R. Butler et al. describes a hydrotreating process which involves sequential desulfurization and dewaxing.
U.S. Pat. No. 3,539,495 issued to C. J. Egan shows an overall refinery flow comprising a hydrocracking step, fractionation and passage of waxy distillate into a two-stage hydrotreating zone which performs dewaxing.
U.S. Pat. No. 4,818,369 issued to R. W. Bortz describes a distillate dewaxing process in which the distillate is passed through a catalytic dewaxing reactor and a hydrotreating reactor in series.
U.S. Pat. No. 4,880,760 issued to R. J. Pellet et al. teaches that hydrocarbon feedstocks can be catalytically hydrodewaxed using a catalyst comprising a nonzeolitic molecular sieve (NZMS). This patent describes the composition and synthesis of a variety of NZMS materials including SAPO and MgAPSO molecular sieves. U.S. Pat. No. 4,793,984 issued to B. M. Lok et al. gives descriptions of NZMS materials including MgAPSO molecular sieves and a generalized description of their use in such processes as hydrofining and hydrocracking.
U.S. Pat. Nos. 4,859,312; 4,921,594 and 5,149,421 issued to S. J. Miller describe the use of a dewaxing catalyst comprising a silicoaluminophosphate (SAPO) molecular sieve and a metal hydrogenation component to treat heavier feedstocks such as middle distillates.
The invention is an integrated hydrotreating process in which a distillate feed stream is first separated into light and heavy middle-distillate boiling range fractions recovered as vapor and liquid fractions respectively. The heavy fraction comprising most of the heavy diesel is passed into a catalytic dewaxing zone while the other fraction is used to quench the effluent of the dewaxing zone to prepare it for processing in a lower temperature aromatics saturation zone.
One embodiment of the invention comprises separating, in a first vapor/liquid separation zone in the presence of added hydrogen as required to obtain the desired separation, a distillate hydrocarbon fraction into a first vapor phase process stream comprising hydrocarbons boiling in the light diesel and kerosene boiling point ranges and a first liquid phase process stream comprising hydrocarbons boiling in the heavy diesel boiling point range; passing the first liquid phase process stream into a catalytic dewaxing zone operated at catalytic hydrodewaxing conditions and thereby producing a catalytic dewaxing zone effluent stream; admixing the first vapor phase process stream and the catalytic dewaxing zone effluent stream and producing a charge mixture having a lower temperature than the catalytic dewaxing zone effluent stream; passing said charge mixture into an aromatic hydrocarbon saturation zone operated at hydrogenation conditions which include a lower temperature than said catalytic hydrodewaxing conditions, and recovering a distillate product stream having a lower pour point and reduced aromatics content than said distillate hydrocarbon fraction.